Low Calorie Diet Beats Running!

Hormonal changes that occur when mice eat significantly
less may help explain an already established phenomenon: a low calorie
diet can extend the lifespan of rodents. And that's a benefit that even
regular exercise does not achieve.

A study called “Effect of exercise and calorie
restriction on biomarkers of aging in mice,” published in the May issue
of the American Journal of Physiology being
lean rather than obese is protective from many diseases.

"But key rodent studies tell us that being lean from
eating less, as opposed to exercising more, has greater benefit for
living longer,” said Derek M. Huffman, the study’s lead author. "This
study was designed to understand better why that is."

Huffman cautions that the study applies only to rodents,
which are different in some key ways from humans. However, at least two
studies which examined people who engage in high-volume exercise versus
people who restricted their calorie intake, - ie ate a low calorie diet - had a similar outcome:
caloric restriction has physiological benefits that exercise alone does
not.

Researchers expect that clues to the physiology of
longevity in mice will eventually be applied to people, Huffman said.

Low Calorie Diet Idea Not New

The study built upon previous studies that showed:

Rats that exercise regularly will,
on average, live longer compared to a group that eats the same amount
but does not exercise. This is because exercise prevents some diseases,
which allows more individual animals to live out their expected life
span.

However, when comparing the rats
in these two groups that eat the same amount, the longest-lived animals
in the exercise group don’t live any longer than the longest-lived rats
in the non-exercise group. Taken together, these findings indicate that
exercise can prevent an early death from disease in some rats, but does
not extend the maximal lifespan of any of the rats.

When comparing rats that exercise
to those that don’t exercise but eat much less, the longest-lived rats
are from the group that ate less.

Two
theories

Taken together, these findings
indicate that caloric restriction protects against disease better than
exercise does, and has the added benefit of extending the life span of
some rats. Physiologists have been trying to unravel the reasons for
this, and two major theories have emerged.

One theory is that exercise
places stress on the body, which can result in damage to the tissues
and DNA. Another theory is that a low calorie diet leads to
physiological changes which benefit the body.

Huffman and his colleagues
designed a study to examine the roles of exercise and caloric
restriction, singly and combined. They controlled for factors such as
weight and the amount of energy expended versus the calories consumed.

They found:

Mice allowed to eat as much as
they wanted had higher insulin levels, regardless of whether they
exercised. That is, how much the mice ate determined their insulin
level, while exercise did not have much effect. High insulin levels are
associated with a risk of diabetes.

The animals that ate as much as
they wanted and did not exercise had the highest levels of insulin-like
growth factor (IGF-1), which plays a key role in regulating cell growth
and cell death. The animals on a low calorie diet had the lowest
levels of IGF-1. Exercise also seemed to play an important role in
regulating IGF-1 levels.

There were some elevated levels of
heat shock proteins, a measure of oxidative stress and possible tissue
damage among the exercising mice. But total protein carbonyls, another
stress measure, were not significantly different.

Both exercise and caloric
restriction moderated the level of 8-hydroxyguanosine (8-OHdG), a
marker of DNA damage. Among the animals that ate all they wanted, those
that did not exercise had the highest levels of 8-OHdG and those that
exercised had much lower levels. The researchers concluded that DNA
damage increases with age and is accelerated by obesity but could be
slowed by a low calorie diet and/or exercise. The researchers noted,
however, that the results may differ if they had used older mice or
subjected them to greater caloric restriction than the mild (9% fewer
calories) or moderate (18%) restriction this study employed.

Overall, these findings
indicate that the physiological stress of exercise did not produce
enough damage to tissues or DNA to explain why exercise does not
lengthen life span. Instead the study suggests that caloric restriction
creates beneficial changes in the body’s hormone levels which exercise
does not. The researchers concluded that these metabolic changes play a
role in extending life.

A handful of studies comparing
calorie restricted people to people who are avid exercisers, found
similar hormonal benefits among those eating less. However, calorie
restriction studies are difficult to carry out in people because
participants often complain of feeling hungry, lethargic, and cold.

Huffman also emphasized that
the benefits of exercise may be greater for humans than for mice
because people are more prone to develop cardiovascular diseases, and
exercise is particularly good at warding off those diseases. Mice tend
to die of kidney disease and cancer, Huffman said.

“I wouldn’t say this study has
direct implications for people right now,” Huffman said. “But it shows
what physiological changes caloric restriction and exercise produce. We
can continue to build upon these findings until we can get a better
understanding of how this works in people.”